Cost

You aren't charged extra

Sprint will bill you for airtime (minutes) for all domestic and international calls made through both Sprint carrier services and Google Voice. Standard airtime and text messaging rates apply based on your contract with Sprint.

When you call other Sprint numbers from your Sprint phone, the calls will be included in your Sprint mobile-to-mobile minutes.

People you call could get charged

If you call someone from a Google Voice number (not a Sprint number), the call might not be included in the other person's mobile-to-mobile minutes. The other person could be charged for the call.